1. Field of the Invention
The present invention relates to an apparatus for generating a trigger pulse (a so-called delayed pulse generator) used to transmit an ultrasonic wave in ultrasonic diagnosis equipment or ultrasonic doppler blood flow measurement equipment.
2. Description of the Related Art
In ultrasonic diagnose or ultrasonic doppler blood flow measurement equipment, offset trigger signals are applied to a plurality of ultrasonic transducing elements of an ultrasonic transducer to trigger them in order to focus or deflect an ultrasonic transmission beam.
In order to generate the offset trigger pulses and apply them to the ultrasonic transducer, the prior art ultrasonic diagnosis equipment comprises, as shown in FIG. 5, a start of transmission reference signal generator 31 for sending a reference pulse signal a to start the transmission, a delay line circuit 32 for converting the reference pulse signal a to a number of transmission start signals b1, b2, b3, . . . , bn which are delayed from each other by a predetermined time, a pulse oscillation circuit 33 for converting the transmission start pulse signals to trigger pulse signals c1, c2, c3, . . . , cn having desired frequencies and numbers of waves, and a transducer drive circuit 34 for converting the trigger pulse signals c1, c2, c3, . . . , cn to high voltage transmission pulse signals d1, d2, d3, . . . , dn. The transmission pulse signals produced by the transducer drive circuit 34 are supplied to a transducer 35 which sends ultrasonic pulses e1, e2, e3, . . . , en to a human body.
The pulse oscillation circuit 33 has n RC burst oscillation circuits which produce the trigger pulse signals c1, c2, c3, . . . , cn by oscillation. The oscillation frequencies of the respective oscillation circuits (the pulse frequencies of the trigger pulse signals) are determined by resistors and capacitors of the oscillation circuits. It is therefore necessary to select the values of the resistors and the capacitors so that the oscillation frequencies meet the desired values.
Waveforms of the pulse signals produced in the apparatus are shown in FIG. 6. The delays in the respective trigger pulse signals which are required for focusing and deflecting the transmission ultrasonic beams are introduced in the conversion by the delay line circuit 32.